This invention relates to a method and a device for manufacturing a belt material for a tire, which is embedded and used, for example, in a pneumatic radial tire.
A pneumatic tire is provided with belts on the radially outer side of a carcass layer to wrap around the carcass layer for improving the cut resistance. While these belts have been manufactured by a large machine provided with a calender, a bias cutter and the like, such a large machine is not suitable for manufacturing numerous types of belts different in specifications these days when the policy of manufacturing many kinds in small volumes is prevailing in the manufacturing industry.
To address the problem as mentioned, a method of manufacturing a flat ribbon-shaped object has conventionally been proposed, for example, as disclosed in Japanese Patent Publication No. Sho 28-3485. This conventional manufacturing method involves winding back yarns from a large number of bobbins mounted on a krill, lining up a group of yarns, spirally winding the group of yarns on a rotary drum formed with spiral parallel grooves on the outer periphery, coating a raw rubber liquid on the wound yarns or rubbing a hard pasty rubber into the wound yarns, heating and vulcanizing the resulting product, and cutting it along the spiral parallel grooves to form the flat ribbon-shaped object.
In the current situation where steel radial tires are mainly used, belts are also made of steel cords. Also, in the belts, linear cords are arranged as obliquely extending at a predetermined angle to the center line of the belt width. In this event, since a tire is a high speed rotating body which receives a dynamic load, the linear cords need be positioned to maintain a lateral balance with respect to the center line of the belt width. For this reason, the belts in the tire are generally comprised of belt materials disposed on the radially outer side, and belt materials disposed on the radially inner side, and these belt materials are arranged such that their linear cords are laterally symmetrically arranged. As to the widths of the belt materials, the belt material on the radially outer side is made narrower than the belt material on the radially inner side.
However, in the conventional manufacturing method, after a group of yarns have been wound around a rotary drum, a raw rubber liquid is coated on or a hard pasty rubber is rubbed into the wound yarns which are then heated and vulcanized. Thus, a wide space is required for installing a krill mounted with a large number of bobbins, thereby giving rise to a problem that the installation space cannot be reduced.
Also, since the linear cords are arranged in a single direction, the conventional manufacturing method has a problem that difficulties are found in applying this method to the manufacturing of a belt of a two-layer structure comprising steel cords as mentioned above.
Further, in the conventional manufacturing method, after a group of yarns has been wound around the outer periphery of a single rotary drum, the group of yarns is cut along the spiral parallel grooves on the rotary drum. This also causes a problem in the inability of a single machine to manufacture two types of belt materials which are different in the direction in which linear cords are arranged on the radially outer side and radially inner side, and in width.
Conventionally, tires have been produced through mass production pointing. For example, wide and elongated sheets are sequentially created, the sheets are cut into a large number of pieces having required dimensions, and the cut sheets are bound to each other in the shape of band which is rolled up for temporary storage as belt materials. The belt materials in stock are sent to a next process. In other words, large sized sheets are fabricated and cut into pieces which are used as belt materials for manufacturing tires.
Apparently, the foregoing mass production system seems to be capable of efficiently manufacturing tires. However, since the mass production system involves manufacturing large sized sheets, and cutting the sheets into belt materials, not only large scaled manufacturing apparatus and cutting apparatus are required for the sheets, but also a space for storing sheets are also required. For this reason, a vast space is required for the factory, and immense energy is also required for operating the factory. Therefore, even if the mass production is oriented, the production cost is increased as a result, thereby failing to benefit from the merit of the mass production. Particularly, when a tire part manufacturing factory is separated from a tire forming factory due to restrictions on geographical conditions, a cost for storing and transporting tire parts accounts for a large proportion of a total cost, so that a reduction in the cost is extremely difficult. Further, since the storage of tire parts, and a transport process intervene between working processes, a variety of problems are involved in quality control regarding the humidity, curing of sheet surfaces, attachment of dusts, and so on, thereby giving rise to a problem of a reduced yield of tire products.